1. Field of the Invention
This invention relates to a data communication method, specifically to a data communication method suitable for use in a camera.
2. Description of Related Art
Due to the recent advancement of automatization of cameras, cameras provided with an auto-focus (AF) system and an auto-exposure (AE) system have increasingly been produced. Nowadays, however, higher function is demanded for a camera. For example, shortening focalizing time or increasing accuracy of focalizing are demanded. Further, various complex kinds of programmed exposure modes, such as a shutter speed priority mode for telephoto lens, an object depth priority mode for wide angle lens, etc., and display apparatuses of a larger size enabling a user to recognize at a glance various photograph information, such as number of frames of film to be photographed, programme mode, etc. are demanded. Further, in order to increase accuracy of focalizing for AF (auto-focus) devices, an increase in the number of CCD's (Charge Coupled Devices), an increase in lens information, and higher calculation processing are required. Under these circumstances, difficulties have been experienced in performing various functions of memorizing, calculating or processing data and controlling a system by means of a single microcomputer.
In order to eliminate the above problems, it will be possible to provide plural microcomputers so as to share the above functions with them. For example, it is possible to provide a main microcomputer, together with one or more of sub-microcomputers, thus entrusting the main microcomputer with a system control function for generally controlling sequential operation of a camera and also controlling a distance measurement and calculation function. In the meantime the main microcomputer may entrust the one or more of sub-microcomputers with a photometric calculation function, a data input control, a data-memorizing function, a display control function, etc. Functions of calculations, control and memorizing may be shared with the plural microcomputers so as to increase processing efficiency.
The above system however requires a large amount of data transmission between the main microcomputer and the sub-microcomputers, and hence it is necessary to allot several communication lines for data communication to the main microcomputer and each of the sub-microcomputers. Furthermore, in order to achieve accurate data transmission, it is necessary to employ a control line such as a communication request line, busy line, or the like, or it may also be necessary to employ a synchronous clock or a system clock for an asynchronous communication with a higher accuracy. Furthermore, a signal for control line communication other than serial transmission lines is required in order to perform serial data communication between the main microcomputer and sub-microcomputers, thus requiring at least three communication lines for performing data communication. Accordingly, unnecessary or excessive use of ports for information processing might occur.
When the user desires to photograph with plural light sources, it is necessary to connect the camera and flash with a cable for exclusive use of plural light sources. This results in time-consuming setting and thus inconvenience. There is another type of system, particularly intended for photographing wild birds, in which such a connection cable is obviated and infrared light is output from an external accessary for remote control, thus releasing the camera from the confines of a cable-type system. In such a type of system, however, only an operation of release is permitted, and thus it is not possible to set up photograph mode and/or exposure rectification from a position remote from the camera body, nor to permit monitoring of number of photographable frames of film and/or brightness of an object.